This invention relates to resin reaction mixtures that are stable during storage and to their preparation and use. Reaction mixtures of polyepoxides and polyisocyanates are becoming more important as starting components for the production of high quality polyaddition plastics. For example, with the aid of curing catalysts, 1,2-epoxides and polyisocyanates may be used to produce plastics having isocyanurate and oxazolidinone structures (DE-AS 1,115,922). Heat hardening resin reaction mixtures for impregnation and embedding are described in U.S. Pat. No. 4,582,723. Such resins are used as electrical insulating materials in numerous applications. Such resins may also be used for the production of rigid structural parts with high dimensional stability under heat. Heat curing resin reaction mixtures containing an organic polyisocyanate, at least one organic compound carrying two epoxide groups, a catalyst which can be activated by heat and optionally other auxiliary agents and additives have already been disclosed in DE-A 3,600,764.
The use of resin reaction mixtures from polyisocyanates and polyepoxides for the synthesis of foam plastics has also been described. E.g., K. Ashida and K. C. Frisch, J. Cell. Plastics, May/June 1972, page 160 et seq. However, the resin reaction mixtures have not been widely used industrially because the mixtures of polyepoxides and polyisocyanates have not been sufficiently stable in storage. A slow increase in viscosity prevents their use in the machines that are generally used today for metering reaction resins in industrial processes. The preparation of fresh resin reaction mixtures necessitates expensive storage methods and rapid processing of the freshly prepared material. It would, therefore, be desirable to obtain storage stable mixtures of polyepoxides and polyisocyanates which do not change their viscosity even when stored for prolonged periods in closed vessels at 40.degree. to 50.degree. C.
An object of the present invention was, therefore, to provide storage stable mixtures of polyepoxides and polyisocyanates which would allow the reaction resins to have a wide application as electrical insulating materials, as foams with high heat resistance, as lacquer binders, as adhesive draw materials, and as matrix materials for construction materials.